Pump Selection for Non-Pressurized System

I'm at the point of selecting a flow center for my DIY geo install and wanted a gut check before pulling the trigger.

I have a 5 ton, single stage Bard HP, and just finished backfilling 6 horizontal slinkies (6x 600' 3/4" loops in parallel).

The HP literature recommends a minimum of 15 GPM, and has a drop of 18.7 Ft of Hd at that rate.
With 20% methanol, the CM worksheet puts me at 10.8 Ft of Hd for the loops. All six loops come through my slab and are headered mere feet away from the HP and planned FC location.

My preference is for a non-pressurized FC, and I really like the B&D QT setups. I was hoping to get away with one 26-99 pump but I think that'll be too marginal (the Reynolds number is right at 2500). I'm now leaning towards a two pump unit with a pair of 26-99's. I see I can get one of these for just shy of $1k; a few hundred bucks more than the single pump. Think that'll do the job?

Incidentally, I do have a good-used pressurized FC I was given that has a pair of 26-116's, but I've read they're power hogs. Perhaps I could sell that to raise a few bucks towards the QT.

yes, non pressurized is the way to go, and the goal is 1 pump, and to make it a 26-99. Whenever I see a 26-116 in a geo system, I know that the designer/installer was clueless about efficiency and not evolved.

Hi and welcome!
If a single 26-99 is marginal I would buy the twin 26-99 and see how it performs with a slightly lower reynolds number. If it works you are home free with a 100% back up pump. If not run both and you are covered.
Eric

We are using variable speed pumps (Groundfos 32-140) even on single or dual stage compressor units, since they run much more efficient, and their pressure curve is right between the 1 and 2 pump 26-99 solution. More expensive, but worth it for me. A single 32-140 would get you about 13.5 gpm, and use about 190 watts running at full speed.

With dual stage heat pumps, the 32-140 would slow down when the compressor is in 1st stage (about 90% of the time) and then use between 35-50 watts.
On the upper end, I rather "starve" the heat pump and use less flow, then overpaying for pumping power.

Thus in my own house, I have a single 26-99 for a 6 ton w-w heatpump. requiring 18 gpm, is happy with 12 gpm. All relative.
I know, the shoemaker runs around barefoot! Did not have time to change it out. Customers first....

Well guys, I guess we'll see how it goes; thanks for the advice. I scored a deal last night on a QT FC with cosmetic defect- dual 26-99's. Planning on getting the system online by the end of the month if all goes well. Now to build the manifolds....

Cadman,
You can remove the one pump and put in blanking plates. Geohyrdosupply sells them. I removed my old pump and put in the blank plate and it increased my flow by .5 or so gpm on the single pump.

Click to expand...

The thought has crossed my mind. I've got some ebay bucks coming due in a couple days and plan to pick up a PP pressure gauge and see what I'm actually working with. It'll be a week or two before I can get my hands on a current clamp and temp probes and then I'll have some numbers to work from.

I made a flowmeter with pvc (j shaped) but for around 50 bucks vs hundreds. Ordered the meter itself from ebay for around 40 bucks. I didn't want to mount it inline with the geo piping. Insert it into the outlet within the flowcenter and the outlet hose goes back down.